1. Field of the Invention
The present invention generally relates to the art of computer database systems, and more specifically to a database system with query relaxation using a Type Abstraction Hierarchy (TAH) as a query condition relaxation structure.
2. Description of the Related Art
Conventional computer databases such as Sybase, Oracle, etc., require a user to have detailed information regarding the data stored in a particular database file. For example, a file or schema for an airline reservation system may include variables or attributes including cost, flight number, departure airport, arrival airport, departure and arrival times, etc.
The attributes for a desired flight are entered into the database as a query, and the database returns an answer in the form of the data for a flight which satisfies the attribute conditions if one exists. If none exist, the database returns a message such as "match not found".
If no exact match is found, the user can relax various attributes based on his or her knowledge of the database until an answer which satisfies sufficiently relaxed conditions is found. For example, if a flight leaving at 10:00 is desired, and none is in the database, a relaxed departure time range of, for example, 9:30 to 10:30 can be manually entered into the query. The database will then return answers corresponding to flights having departure times within the specified range.
The file for the exemplary airline reservation system has a number of attributes (e.g. departure time, arrival time) which can be independently relaxed. The user must decide which attributes are more important than others, and within which ranges, in order to query the database to obtain an answer which is most desirable in view of the individual considerations. This requires knowledge and skill which must be obtained through considerable experience. Even with such knowledge and skill, manual manipulation of the database conditions is a time consuming and inherently "hit or miss" operation.
Conventional databases return only exact values or instances. They are not capable of returning approximate answers or processing conceptual queries. An example of the latter would be to locate a flight which arrives at a city "NEAR" New York at "APPROXIMATELY" 9:00.
In view of the above, a need exists in the art for a system for managing a conventional database which automates the process of progressively relaxing attributes until an acceptable answer is obtained. A further need exists for a system which is able to obtain approximate answers from a database, and to process conceptual queries.